This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. EPR (also referred to as Electron Spin Resonance) spectroscopy is based on absorption of microwave energy by free radicals or paramagnetic species in the presence of an external electromagnetic field resulting in the transition of electron spin states. Dr. Zimmerman's laboratory in the Department of Cellular and Integrative Physiology at UNMC houses a Bruker E-Scan Table Top EPR spectrometer (see figure). In combination with EPR-detectable, radical-sensitive cyclic hydroxylamines, often referred to as "spin probes", the E-Scan can be and has been used to measure levels of free radicals (e.g. superoxide, hydroxyl radical) in various biological samples including cultured cells, culture media, blood, and isolated tissue.